Structure and system for simultaneous sensing a magnetic field and mechanical stress

ABSTRACT

A structure having collocated magnetic field sensing elements can be used to simultaneously determine magnetic field and mechanical stress. A primary magnetic field sensing element generates a primary signal responsive to a magnetic field and a secondary magnetic field sensing element generates a secondary signal responsive to mechanical stress. A system includes a stress compensation module to receive the primary and signals, and to compensate for mechanical stress in the primary signal.

FIELD OF THE INVENTION

This invention relates generally to magnetic field sensors and, moreparticularly, to magnetic field sensors having circuitry to sense andadjust a sensitivity of the magnetic field sensors to a magnetic field.

BACKGROUND

Magnetic field sensors employ a variety of types of magnetic fieldsensing elements, for example, Hall effect elements andmagnetoresistance elements, often coupled to a variety of electronics,all disposed over a common substrate. A magnetic field sensing element(and a magnetic field sensor) can be characterized by a variety ofperformance characteristics, one of which is a sensitivity, which can beexpressed in terms of an output signal amplitude versus a magnetic fieldto which the magnetic field sensing element is exposed.

The sensitivity of a magnetic field sensing element, and therefore, of amagnetic field sensor, is known to change in relation to a number ofparameters. For example, the sensitivity can change in relation to achange in temperature of the magnetic field sensing element. As anotherexample, the sensitivity can change in relation to a mechanical stress(or “strain”) imposed upon the substrate over which the magnetic fieldsensing element is disposed. Such stress can be imposed upon thesubstrate at the time of manufacture of an integrated circuit containingthe substrate. For example, the strain can be imposed by stresses causedby curing of molding compounds used to form an encapsulation of thesubstrate, e.g., a plastic encapsulation.

It will be recognized that changes in the temperature of a magneticfield sensor can directly result in changes of sensitivity due to thechanges of temperature. However, the changes in the temperature of themagnetic field sensor can also indirectly result in changes ofsensitivity where the temperature imparts strains upon the substrateover which the magnetic field sensing element is disposed.

The changes in sensitivity of the magnetic field sensor and of themagnetic field sensing element are undesirable.

SUMMARY

A magnetic field sensor, which includes a magnetic field sensingelement, can measure, either directly or indirectly, a sensitivity ofthe magnetic field sensing element, and can adjust a sensitivity of themagnetic field sensor accordingly. Therefore, the magnetic field sensormaintains a sensitivity to magnetic fields that is generally invariantin the presence of temperature excursions or in the presence ofmanufacturing steps, both of which might otherwise tend to change thesensitivity of the magnetic field sensor . . . .

In accordance with one aspect of the invention, a magnetic field sensorcomprises a first magnetic field sensing element supported by asubstrate, the first magnetic field sensing element having a firstsensitivity to a magnetic field and a first sensitivity to mechanicalstress in the substrate, the first magnetic field sensing element forgenerating a first output signal responsive to the magnetic field, thefirst magnetic field sensitivity, mechanical stress in the substrate,and the first mechanical stress sensitivity; a second magnetic fieldsensing element supported by the substrate, the second magnetic fieldsensing element having a second sensitivity to the magnetic field and asecond sensitivity to mechanical stress in the substrate, the secondmagnetic field sensing element for generating a second output signalresponsive to the magnetic field, the second magnetic field sensitivity,the mechanical stress in the substrate, and the second mechanical stresssensitivity; a stress compensation module operatively coupled to receivea first stress compensation input signal responsive to the first outputsignal and a second stress compensation input signal responsive to thesecond output signal and to generate a stress compensation signal; andan adjustable gain stage coupled to amplify the first output signal witha gain in accordance with the stress compensation signal to generate astress-compensated output signal, wherein the stress-compensated outputsignal is responsive to the magnetic field, and is generally notresponsive to the mechanical stress in the substrate.

In some embodiments, the stress compensation module is configured tocalculate the gain using the first magnetic field sensitivity, thesecond magnetic field sensitivity, the first mechanical stresssensitivity, and the second mechanical stress sensitivity, wherein thestress compensation signal is based upon the gain.

In certain embodiments, the second mechanical stress sensitivity isapproximately zero. The stress compensation module may be configured tocalculate the gain using the first magnetic field sensitivity and thesecond magnetic field sensitivity, wherein the stress compensationsignal is based upon the gain.

In various embodiments, the magnetic field sensor further comprises afirst amplifier coupled to receive the first output signal and togenerate the first stress compensation input signal and a secondamplifier coupled to receive the second output signal and to generatethe second stress compensation input signal. The first and second outputsignals may be responsive to a substrate temperature and the first andsecond stress compensation signals are generally not responsive to thesubstrate temperature. The magnetic field sensor may further include athreshold detector coupled to receive a threshold level signal and athreshold detector input signal responsive to the first output signal,the threshold detector configured to generate an enabling signal basedupon the threshold level signal and the threshold detector input signal.

In some embodiments, the stress compensation module is coupled toreceive the enabling signal and configured to calculate the gain inresponse to the enabling signal.

According to another aspect of the invention, a dual Hall elementcomprises a substrate having a bottom surface and a top surface; anN-type epitaxial layer disposed over the substrate top surface, theepitaxial layer having a top surface and a bottom surface; a barrierstructure disposed over the substrate and extending perpendicular fromthe epitaxial layer top surface so as to form a barrier to electricalcharges within the epitaxial layer and resulting in a bounded region ofthe epitaxial layer having a generally octagonal shape; a P-well regiondiffused into the epitaxial layer; and a plurality of pickups implantedand diffused into the epitaxial layer, opposing pairs of the pluralityof pickups separated by the P-well region, each one of the plurality ofpickups comprising an N+ type diffusion, wherein a first set of theplurality of pickups is operable to form a first Hall element and asecond different set of the plurality of pickups is operable to form asecond Hall element.

According to another aspect of the invention, a dual Hall elementcomprises a substrate having a bottom surface and a top surface; anN-type epitaxial layer disposed over the substrate top surface, theepitaxial layer having a top surface and a bottom surface; a barrierstructure disposed over the substrate and extending perpendicular fromthe epitaxial layer top surface so as to form a barrier to electricalcharges within the epitaxial layer; a P-well region diffused into theepitaxial layer; a first plurality of pickups implanted and diffusedinto the epitaxial layer, opposing pairs of the first plurality ofpickups separated by the P-well region, each one of the first pluralityof pickups comprising an N+ type diffusion; and a second plurality ofpickups implanted and diffused into the P-well region, each one of thesecond plurality of pickups comprising an P+ type diffusion, wherein thefirst plurality of pickups is operable to form a first Hall element andthe second plurality of pickups is operable to form a second Hallelement.

According to another aspect of the invention, a dual Hall elementcomprises a bottom structure including: a substrate having a bottomsurface and a top surface; an N-type epitaxial layer disposed over thesubstrate top surface, the epitaxial layer having a top surface and abottom surface; a barrier structure disposed over the substrate andextending perpendicular from the epitaxial layer top surface so as toform a barrier to electrical charges within the epitaxial layer; aP-well region diffused into the epitaxial layer; and a first pluralityof pickups implanted and diffused into the epitaxial layer, opposingpairs of the first plurality of pickups separated by the P-well region,each one of the first plurality of pickups comprising an N+ typediffusion; and a top structure electrically isolated from the bottomstructure via an isolation region, the top structure including: a toplayer; and a second plurality of pickups implanted and diffused into thetop layer, wherein the first plurality of pickups is operable to form afirst Hall element and the second plurality of pickups is operable toform a second Hall element.

In some embodiments, the top layer comprises a poly silicon material. Incertain embodiments, each one of the second plurality of pickupscomprises a P+ type diffusion. In some embodiments, each one of thesecond plurality of pickups comprises a N+ type diffusion.

According to another aspect of the invention, a dual Hall elementcomprises a substrate having a bottom surface and a top surface; anP-type epitaxial layer disposed over the substrate top surface, theepitaxial layer having a top surface and a bottom surface; an N-wellregion diffused into the epitaxial layer; a P-well region diffused intothe N-well region; a first plurality of pickups implanted and diffusedinto the N-well region, opposing pairs of the first plurality of pickupsseparated by the P-well region, each one of the first plurality ofpickups comprising an N+ type diffusion; and a second plurality ofpickups implanted and diffused into the P-well region, each one of thesecond plurality of pickups comprising an P+ type diffusion, wherein thefirst plurality of pickups is operable to form a first Hall element andthe second plurality of pickups is operable to form a second Hallelement.

According to another aspect of the invention, a dual Hall elementcomprises: a substrate having a bottom surface and a top surface; anN-type epitaxial layer disposed over the substrate top surface; a firstplanar Hall element disposed within or over the epitaxial layer, thefirst planar Hall element having a first plurality of pickups with afirst center between the first plurality of pickups; and a second planarHall element disposed within or over the epitaxial layer, the secondplanar Hall element having a second different plurality of pickups witha second center between the second plurality of pickups, wherein thefirst and second centers are substantially collocated.

BRIEF DESCRIPTION OF THE DRAWINGS

The structures and techniques sought to be protected herein may be morefully understood from the following detailed description of thedrawings, in which:

FIG. 1 is block diagram of an illustrative magnetic field sensor havinga dual magnetic field sensing element, here a dual Hall effect element,coupled to a stress-compensation circuit;

FIG. 2 is a top-view of an illustrative dual Hall effect element havingtwo sets of pickups separated by a P-well region;

FIG. 2A is a side-view of the dual Hall effect element of FIG. 2;

FIG. 3 is a top-view of another illustrative dual Hall effect elementhaving one set of pickups separated by a P-well region and one set ofpickups disposed within the P-well region;

FIG. 3A is a side-view of the dual Hall effect element of FIG. 3;

FIG. 4 is a top-view of yet another illustrative dual Hall effectelement having one set of pickups separated by a P-well region and oneset of pickups disposed upon a top structure deposited on top of theP-well region;

FIG. 4A is a side-view of the dual Hall effect element of FIG. 4;

FIG. 5 is a top-view of another illustrative dual Hall effect elementcomprising an N-type inversion layer diffused into a P-type epitaxialregion; and

FIG. 5A is a side-view of the dual Hall effect element of FIG. 5.

The drawings are not necessarily to scale, or inclusive of all elementsof a system, emphasis instead generally being placed upon illustratingthe concepts, principles, systems, and techniques sought to be protectedherein.

DETAILED DESCRIPTION

Before describing the present invention, some introductory concepts andterminology are explained. As used herein, the term “magnetic fieldsensor” is used to describe a circuit (which can include packagingthereof) that includes a “magnetic field sensing element.” Magneticfield sensors are used in a variety of applications, including, but notlimited to, a current sensor that senses a magnetic field generated by acurrent flowing in a current conductor, a magnetic switch that sensesthe proximity of a ferromagnetic object, a rotation detector that sensespassing ferromagnetic articles, for example, magnetic domains of a ringmagnet, and a magnetic field sensor that senses a magnetic field densityof a magnetic field. The term “magnetic field sensor” is usedinterchangeably herein with the phrase “circuit for sensing a magneticfield.”

Hall effect elements are one type of magnetic field sensing elements. Asis known, there are different types of Hall effect elements, forexample, a planar Hall element, a vertical Hall element, and a CircularVertical Hall (CVH) element. Magnetic field sensing elements are shownand described below to be planar (i.e., horizontal) Hall effectelements.

As used herein, the term “substrate” is used to describe any type ofstructure with a flat surface upon which semiconductor materials can bedeposited and/or into which semiconductor materials can be implanted anddiffused. In some embodiments, the substrate is a P-type siliconsubstrate having a particular range of concentrations of P-type atoms(i.e., ions).

A prior art planar (i.e., horizontal) Hall effect element is known tohave four terminals. A current is driven between two opposing ones ofthe four terminals, and a differential voltage signal is generated as anoutput signal at the other two terminals. The differential voltagesignal is responsive to a magnetic field.

The prior art planar Hall effect element can be used with so-called“current spinning”, also referred to as “chopping.” With currentspinning, different opposing ones of the four terminals are used insequence as the current driven terminals and different ones of the fourterminals are used in the sequence as the output signal terminals.

The prior art Hall effect element, from a top view, can have a varietyof shapes bounded by electrical isolation structures in a siliconsubstrate. Typically, the prior art Hall effect element has a squareshape from a top view.

In contrast to the prior art Hall effect element, the term “dual Halleffect element” is used herein to describe a semiconductor structurehaving both a primary Hall effect element with at least four contactsand secondary Hall effect element with another at least four contacts.The primary and secondary Hall effect elements are collocated (e.g.,overlaid) with each other such that the secondary Hall effect elementlies within or over a perimeter of the primary Hall effect element, theperimeter defined by an outer boundary of an electrical isolationstructure surrounding the primary Hall effect element. The primary andsecondary Hall effect elements are arranged so as to be coincident inthe direction of maximum magnetic field sensitivity and can beconsidered to be substantially collocated. In some embodiments, theprimary and secondary Hall effect elements share a common isolationstructure.

In some embodiments, at least one of the primary Hall effect element orthe secondary Hall effect element can be used with currentspinning/chopping.

As used herein, the term “epi” is used to refer to an epitaxial layer,for example, an N-type epitaxial layer, disposed over a substrate, forexample, a P-type substrate, and having a particular range ofconcentrations of N-type atoms (i.e. ions). As used herein, the term“N+” or “NP” is used to refer to a region implanted and diffused into asemiconductor layer, for example, into a surface of the epitaxial layerfurthest from the substrate, and having another particular range ofconcentrations of N-type atoms (i.e. ions).

As used herein, the term “P-well” is used to refer to a region implantedand diffused into a semiconductor layer, for example, into a surface ofthe epitaxial layer furthest from the substrate, and having a particularrange of concentrations of P-type atoms (i.e. ions). As used herein, theterm “P-type barrier layer” or simply “PBL” is used to refer to a regionimplanted and diffused into a semiconductor layer, for example,implanted into the substrate and then upwardly diffused into theepitaxial (epi) layer. The epi layer can be grown after PBL implant anddiffusion steps, and the upward diffusion into epi layer can beperformed during a field oxidation process.

As used herein, the term “N-well” is used to refer to a region implantedand diffused into a semiconductor layer, for example, into a surface ofthe epitaxial layer furthest from the substrate, and having a particularrange of concentrations of N-type atoms (i.e. ions).

As used herein, the term “P+” or “PP” is used to refer to a regionimplanted and diffused into a semiconductor layer, for example, into asurface of the epitaxial layer furthest from the substrate, and havinganother particular range of concentrations of P-type atoms (i.e. ions).

As used herein, the concentrations of the above types of semiconductorstructures fall into the following ranges:

-   -   substrate: about 1×10¹⁵ P-type atoms per cm³, for example, boron        atoms;    -   n-type epi: about 5×10¹⁴ to about 1×10¹⁶ N-type atoms per cm³,        for example, Arsenic atoms, where: 5×10¹⁴ can be representative        of a concentration of epi bulk doping, and 1×10¹⁶ can be        representative of a concentration at a surface region of the epi        layer at about 2 um depth created by an additional epi implant        step (Alternatively, 1×10¹⁵ to 6×10¹⁵);    -   P-type epi: about 1×10¹⁶ to 5×10¹⁶ atoms per cm³, for example,        boron atoms;    -   N+: about 1×10²⁰ N-type atoms per cm³, for example, phosphorous        atoms;    -   P-well: about 6×10¹⁶ to 2×10¹⁷ P-type atoms per cm³ or about        5×10¹⁷ to 1×10¹⁸ P-type atoms per cm³ for example, boron atoms;    -   N-well: about 3×10¹⁶ to 1×10¹⁷N-type atoms per cm³, for example,        boron atoms;    -   PBL: about 1×10¹⁸ to about 2×10¹⁸ P-type atoms per cm³, for        example, boron atoms; and    -   P+: about 3×10¹⁹ to about 5×10¹⁹ P-type atoms per cm³, for        example, boron atoms.

In some embodiments, the concentrations are outside of the above rangesor values, but within about +/− twenty percent of the above ranges orvalues.

Before describing the present invention, it should be noted thatreference is sometimes made herein to assemblies having a particularshape (e.g., square or octagonal). One of ordinary skill in the art willappreciate, however, that the techniques described herein are applicableto assemblies having a variety of sizes and shapes.

Referring to FIG. 1, an illustrative magnetic field sensor 100 forsensing a magnetic field includes a dual magnetic field sensing element102 comprising magnetic field sensing elements 102 a, 102 b. In variousembodiments, the dual magnetic field sensing element 102 is a dual Halleffect element 102 comprising a primary Hall effect element 102 a and asecondary Hall effect element 102 b. The primary and secondary Halleffect elements 102 a, 102 b are coupled to receive drive currents fromrespective current sources (not shown) and configured to generaterespective primary and secondary output signals 104, 106 sensitive to anapplied magnetic field 108.

In some embodiments, each one of the output signals 104, 106 is adifferential signal. Accordingly, the amplifiers 110, 112 may comprisedifferential amplifiers.

It should be understood that the signals 104, 106 (along with variousother signals shown in FIG. 1 and described herein) are carried viarespective signal paths shown in FIG. 1 using identical referencedesignators. For simplicity of explanation, signals and their respectivesignal paths are referred to interchangeably herein.

In embodiments, the primary and secondary Hall effect elements 102 a,102 b are provided within a common structure 102. The common structure102 may comprise a dual Hall effect element supported by a commonsubstrate and also disposed within or over a common outer electricalisolation barrier.

In the embodiment shown, the primary output signal 104 is coupled to afirst amplifier 110 to generate a primary (or “first”) amplified signal114 and the secondary output signal 106 is coupled to a second amplifier112 to generate a secondary (or “second”) amplified signal 116. In someembodiments, the gain of amplifiers 110 and/or 112 is based on a trimvalue stored in programmable memory, such as erasable programmableread-only memory (EEPROM).

The primary and secondary amplified signals 114, 116 are operativelycoupled to a stress compensation module 118 and are therefore alsoreferred to as first and second stress compensation input signals 114,116, respectively. In other embodiments, amplifiers 110 and/or 112 maybe omitted and, thus, the first and second stress compensation inputsignals 114, 116 correspond to primary and secondary output signals 104,106, respectively.

The stress compensation circuit 118 processes the input signals 114, 116to generate a gain compensation signal 120. The gain compensation signal120 is coupled to an adjustable gain stage 122 to modulate (i.e., changea gain of) an output voltage from the primary Hall effect element 102 ato generate a stress-compensated output signal 124. In the embodimentshown, amplified signal 114 is modulated by the adjustable gain stage122; in other embodiments, the primary output signal 104 is modulated.The gain compensation signal 120 results in a control of a sensitivityof the magnetic field sensor 100, as described herein below.

In some embodiments, the magnetic field sensor 100 further comprises athreshold detector 126. The threshold detector 126 may be coupled toreceive a threshold level signal 128 and the primary amplified signal114, and configured to generate an enabling signal 130, which may becoupled as input to the stress compensation module 118. If the primaryamplified signal 114 exceeds a threshold level indicated by thethreshold signal 128, the generated enabling signal 130 has a firststate (e.g., non-zero voltage value); otherwise the generated enablingsignal 130 has a second different state (e.g., zero voltage).

The stress compensation module 118 includes any combination of hardwareand/or software configured to operate as described herein below. In someembodiments, the stress compensation module 118 comprises anapplication-specific integrated circuit (ASIC). In other embodiments,the stress compensation module 118 comprises a processor configured toread and execute software instructions. In some embodiments, the stresscompensation module 118 can be embodied in a discrete electroniccircuit, which can be an analog or digital. In the embodiment shown, thestress compensation module 118 includes programmable memory 118 a (e.g.,EEPROM) and volatile memory 118 b.

The output voltage of a Hall element is proportional to the magneticfield times the element's field sensitivity. Ideally, the fieldsensitivity is a constant value. However, in realistic operationconditions, the magnetic field sensitivity of a Hall effect element canvary (or “shift”) with temperature and/or due to mechanical stresses inthe substrate. Accordingly, the output voltage of the primary andsecondary Hall effect elements 102 a, 102 b (i.e., the primary andsecondary output signals 104, 106) may have sensitivities that arechanged by temperature- and/or stress-induced sensitivity shifts.

Any suitable technique can be used to compensate for temperature-inducedsensitivity shifts. For example, prior to general operation, thesensitivity shift of each Hall element 102 a, 102 b can be measured atseveral different temperatures. Such measurements can be stored inprogrammable memory (e.g., EEPROM) and used to adjust to gain ofamplifiers 110, 112 based on a current temperature, thereby correctingfor temperature-induced sensitivity shift.

Assuming that temperature-induced sensitivity shifts have been correctedand ignoring offset effects, the output voltage for a given Hall elementis approximately equal to the product of the magnetic field B and thefield sensitivity of the Hall element, modulated by (i.e., changed by)the product of the stress and the stress sensitivity. Formally, theoutput voltage of the primary Hall element 102 a can be expressed as:V ₁ =B×field_sensitivity₁×[1+(stress×stress_sensitivity₁)]  (1)and the output voltage of the secondary Hall element 102 b can beexpressed as:V ₂ =B×field_sensitivity₂×[1+(stress×stress_sensitivity₂)]  (2)where:

-   -   B corresponds to a strength of the magnetic field 108,    -   stress corresponds to mechanical stress in the substrate,    -   field_sensitivity₁ is the sensitivity of the primary Hall        element 102 a to the magnetic field,    -   stress_sensitivity₁ is the sensitivity of the primary Hall        element 102 a to stress,    -   field_sensitivity₂ is the sensitivity of the secondary Hall        element 102 b to the magnetic field, and    -   stress_sensitivity₂ is the sensitivity of the secondary Hall        element 102 b to mechanical stress.

In the above equations, it is assumed that the magnetic fieldsensitivities (i.e., field_sensitivity₁ and field_sensitivity₂) havebeen corrected for temperature-induced shifts. As discussed above, thiscan be achieved by controlling the gain of amplifiers 110, 112. Thus, insome embodiments, the primary Hall output voltage V₁ may correspondsignal 114 and the secondary Hall output voltage V₂ may correspond tosignal 116. In other embodiments, the primary Hall output voltage V₁ maycorrespond signal 104 and the secondary Hall output voltage V₂ maycorrespond to signal 106.

From equations (1) and (2), the stress can be determined as follows:

$\begin{matrix}{{stress} = \frac{\begin{bmatrix}{\left( {{field\_ sensitivity}_{2} \times V_{1}} \right) -} \\\left( {{field\_ sensitivity}_{1} \times V_{2}} \right)\end{bmatrix}}{\begin{bmatrix}{\left( {{field\_ sensitivity}_{1} \times V_{2} \times {stress\_ sensitivity}_{1}} \right) -} \\\left( {{field\_ sensitivity}_{2} \times V_{1} \times {stress\_ sensitivity}_{2}} \right)\end{bmatrix}}} & (3)\end{matrix}$and the undesirable stress effects can be compensated for by modulatingthe primary output voltages 104 by a gain calculated as follows:gain=1/[1+(stress×stress_sensitivity₁)]  (4)

In the case where the secondary Hall effect element 102 b is generallyimmune to stress effects (i.e., stress_sensitivity₂≅0), a gain isindependent of stress and stress sensitivities and can be determined as:gain=(field_sensitivity₁ ×V ₂)/(field_sensitivity₂ ×V ₁)  (5)

In equation (5), the gain is proportional to V₂ (i.e., the secondaryoutput voltage 106). Accordingly, error in V₂ leads to proportionalerror in the gain and error, as a percentage, is most pronounced when V₂is small (i.e., when the gain of the secondary Hall element 102 b islow). Thus, it makes sense to update the correction factor (gain) onlywhen the magnitude of V₂ is substantially larger then the error inV₂—i.e., in the case of a high signal-to-noise ratio (SNR).

One approach for achieving high SNR is to ensure a sufficiently largemagnetic field B by comparing a Hall output voltage to a thresholdvalue. For example, the primary Hall output voltage (signal 104 or 114)can be compared to a threshold level 128 using threshold detector 126.Another approach for achieving high SNR is to ensure a sufficientlysmall error by limiting the bandwidth of output signals 104, 106.Assuming the errors are not disproportionally concentrated in thebandwidth where the output voltages are being measured, this approachworks well for thermal noise and other environment noise, however caremust be taken to limiting the impact of sampling noise effects. Anysuitable filtering techniques may be used for bandwidth limiting. Insome embodiments, the Hall output voltages have a bandwidth between 100KHz and 1 MHz, and the stress compensation module input signals 114, 116have a bandwidth between 1 Hz and 100 Hz. It will be appreciated thatthere is a balance between the strength of the magnetic field B and thesignal bandwidth. If the field is strong, wider bandwidths can be usedand a short duration is necessary to achieve sufficiently high SNR. Onthe other hand, if the magnetic field is weak, a narrower bandwidthshould be used to achieve high SNR.

During operation, the primary and secondary Hall effect elements 102 a,102 b are assumed to be subject to generally the same mechanical stress,in particular, because they are substantially collocated. In addition,the primary and secondary Hall effect elements 102 a, 102 b can bearranged so that respective directions of maximum magnetic fieldsensitivity are substantially parallel to each other.

In embodiments, the magnetic field sensitivities and the stresssensitivities are unique for each Hall element 102 a, 102 b. In someembodiments, the products stress_sensitivity₁× field_sensitivity₂ andstress_sensitivity₂× field_sensitivity₁ are unique.

The magnetic field sensitivity values field_sensitivity₁ andfield_sensitivity₂ and/or the stress sensitivity valuesstress_sensitivity₁ and stress_sensitivity₂ can be determined prior tooperation and stored in programmable memory 118 a.

In operation, the Hall effect elements 102 a and 102 b generaterespective output signals 104 and 106 in response to a magnetic field108. The output signals 104 and 106 may be trimmed and/or corrected fortemperature-induced sensitivity shift via respective amplifiers 110 and112. The resulting amplified signals 114 and 116 are provided as inputto the stress compensation module 118. Using the a priori sensitivityvalues (e.g., values stored in programmable memory 118 a), thecompensation module 118 may apply equation (3) to determine mechanicalstress and calculate a gain compensation value using equation (4) togenerate gain compensation signal 120. Alternatively, in the case wherethe secondary Hall effect element 102 b is generally immune to stresseffects (i.e., stress_sensitivity₂≅0), the compensation module 118 maycalculate a gain directly using equation (5) to generate gaincompensation signal 120. In turn, the adjustable gain stage 122 canmodulate an output voltage from the primary Hall effect element 102 a(i.e., signal 104 or signal 114) with the gain compensation signal 120to generate a stress-compensated output signal 124.

It should be appreciated that the stress-compensated output signal 124is responsive to the strength of the magnetic field 108 multiplied bythe magnetic field sensitivity of the primary Hall effect element 102 aand is generally not responsive to the effects of temperature andmechanical stress.

In certain embodiments, the stress compensation module 118 updates thegain compensation value and corresponding gain compensation signal 120in a continuous manner, meaning that the input signals 114 and 116 arecontinuously evaluated—i.e., using equations (3) and (5), or equation(5)—to determine a gain, and that the gain compensation signal 120 iscontinuously updated based on the gain.

In other embodiments, the stress compensation module 118 updates thegain compensation value and corresponding gain compensation signal 120in a discontinuous manner.

If the inputs 114, 116 to the stress compensation module have low SNR,then the resulting gain compensation signal 120 could be effectivelyrandom (i.e., close to 100% in error) resulting in poor measurementsfrom the circuit 100. As discussed above, one approach to preventingsuch measurement errors is to ensure that the primary Hall outputvoltage (i.e., signal 104 or signal 114) exceeds a threshold value.Accordingly, in some embodiments, the stress compensation module 118recalculates the stress and gain compensation signal 120 only when thethreshold detector 126 indicates this condition via enabling signal 130.

In addition to minimizing measurement errors, it may be desirable tothrottle the rate at which the gain compensation signal is recalculatedso as to reduce average power consumption. Between updates, the stresscompensation module 118 may store the previous calculated gaincompensation value in volatile memory 118 b. If the case of infrequentupdates, it may be preferable to re-calculate the gain compensationrather than use an obsolete stored value. Thus, in some embodiments atimer is provided to expire the stored gain compensation value after apredetermined amount of time.

Referring to FIGS. 2 and 2A together, for which FIG. 2 shows a top viewof FIG. 2A, and in which like elements are shown having like referencedesignations, an illustrative dual Hall effect element 200 may be thesame as or similar to the dual Hall effect element 102 of FIG. 1. Theillustrative dual Hall effect element 200 may be representative of aHall plate at an intermediate step of integrated circuit fabrication. Inparticular, the dual Hall effect element 200 does not show additionallayers and structures that may be formed over a typical Hall effectelement. In addition, the dual Hall effect element 200 does not showsome structures that are temporary, for example, photo resist masks,which can be removed during the fabrication process. Accordingly,reference may be made below to patterning that uses photo resist masksto provide openings for implant steps. However, in other instancesdescribed below, a field oxide layer can be used to provide openings forsome implant and diffusion steps.

The dual Hall effect element 200 can be constructed over a substrate203, in particular, within and upon an epitaxial (“epi”) region (or“layer”) 202 disposed upon the substrate 203. In this example, the epiregion 202 is an N-type epi region. The dual Hall effect element 200includes a plurality of pickups 208 (with eight pickups 208 a-208 hshown in this example) implanted and diffused into the epi region 202.In some embodiments, one or more of the plurality of pickups 208comprises an N+ type diffusion.

It will be appreciated that the dual Hall effect element 200 is a dualplanar (i.e., horizontal) Hall effect element. As is known in the art,planar Hall elements have an axis of maximum magnetic field sensitivitythat is perpendicular to a substrate on which the planar Hall element isformed.

In certain embodiments, the dual Hall effect element 200 includes aninner P-well region 204 diffused into the epi region 202, as shown.Opposing pairs of pickups (e.g., pickups 208 a and 208 e) may beseparated by the inner P-well region 204. It will be understood thatincluding an inner P-well region 204 may provide certain advantages. Inoperation, the inner P-well region 204 tends to cause the currentflowing between opposing pairs of pickups to flow under the P-wellregion 204. As is known, Hall sensitivity is proportional to carriermobility, which is inversely related to dopant density. Since the dopantdensity is highest near a surface 212 of the epi region 202, the currentwould (without the P-well region 204) tend to flow nearer the surface212, resulting in a relatively low Hall sensitivity. Thus, the P-wellregion 204 forces currents lower in the epi region 202 (i.e., closer tothe substrate 203) where mobility is higher, thus improving thesensitivity of the planar Hall element. In some embodiments, the epiregion 202 has a generally uniform, low dopant-density, and thus aP-well region 204 is unnecessary.

In the side-view of FIG. 2A, pickups 208 g and 208 c are visible,pickups 208 d-208 f are not visible, and pickups 208 h, 208 a, and 208 bare hidden behind the inner P-well region 204.

As used herein, the term “pickup” is used to describe an active region,here and N+ active region, implanted and diffused into a semiconductorstructure, i.e., into an outer surface of the epi region 202, and whichis used to provide an area at which an electrical signal is receivedfrom the semiconductor structure or at which an electrical signal isinput to the semiconductor structure. In particular, a pickup (e.g.,pickup 208 a) is an active or device region first defined by a “device”photo resist mask, which is thereafter removed.

Associated with each one of the pickups (e.g., pickup 208 a) is aso-called “contact,” of which contacts 210 c, 201 g are representative.As used herein, the term “contact” is used to describe a metallizedconnection of a semiconductor structure, for example, metal plating orlayer (not shown) over contact openings. A contact (e.g., contact 210 c)provides a low resistance electrical coupling to a corresponding pickup(e.g., pickup 208 c). While one contact is shown for each pickup, inother embodiments, there can be a plurality of contacts in electricalcommunication with an associated pickup. In some embodiments, associatedwith and electrically coupled to each one of the contacts 210, is ametal structure. Such a metal structure may correspond to a portion of ametal layer of a semiconductor structure used to provide a lowresistance electrical coupling to a contact.

An outer horizontal boundary of the epi region 202 is determined by aninner edge (closest to the pickups 208) of an outer P-well region 206that surrounds the pickups 208. The outer P-well region 206 is implantedand diffused into the epi region 202 from a top surface of the epiregion 202 (i.e., the surface furthest from the substrate 203). It willbe understood that the edges of the outer P-well region 206 may bealtered as the region 206 is diffused during fabrication of the dualHall effect element 200. In some embodiments, the outer P-well region206 results from an implant formed in conjunction with a photo resistmask that provides openings for the implantation, and which is laterremoved. In some embodiments, the P-well implant is performed prior togrowth of a field oxide layer.

A PBL structure 207 is diffused within the epi region 202 and over thesubstrate 203 before placement of the epi region 202. It will beunderstood that the edges of the PBL structure 207 may be altered as theregion 206 is diffused during fabrication of the dual Hall effectelement 200. The PBL structure 207 joins with or merges with the outerP-well region 206 forming a barrier structure (or “isolation region”)213 to electrical isolate charges that move within the epi region 202during operation of the dual Hall effect element 200.

Placement of a device photo resist mask (not shown) and implantation ofthe pickups 208 can be preceded by formation of a field oxide layer (notshown) over a top surface 212 of the epi region 202. Openings can beprovided (i.e., etched) through the field oxide layer by way of thedevice photo resist mask, the openings for implantation of the pickups208. Openings through the field oxide layer may be provided over theouter P-well region 206 for a masked P+ implant.

The illustrative dual Hall effect element 200 includes a major planarsurface (shown in FIG. 2) that can have an outer perimeter 214 having agenerally octagonal shape. The outer perimeter 214 is comprised of eightsides 214 a-214 h of generally equal length. The sides 214 a-214 h aredefined by edges of the respective epi regions 202 bounded by respectiveisolation regions 213, for example by outer P-well region 206 and PBLstructure 207. In addition, the dual Hall effect element 200 includes aninner perimeter 216 also having a generally octagonal shape, whichperimeter 216 is defined by a boundary between the inner P-well region204 and the epi region 202. The inner perimeter 216 can be comprised ofeight sides 216 a-216 h of generally equal length. In embodiments, arepresentative outer side 214 a has a length between 60-100 microns, anda representative inner side 216 a has a length between 40-80 microns.The outer and inner octagonal perimeters 214, 216 may be aligned suchthat each outer side 214 a-214 h is generally parallel to one of theinner sides 216 a-216 h. The outer and inner octagonal perimeters 214,216 may also be aligned such that centers of the outer and inneroctagonal perimeters 214, 216 (i.e., centers of the first and secondsets of pickups 208 a, 208 c, 208 e, 208 g and 208 b, 208 d, 208 f, 208h) are substantially collocated.

In some embodiments, ones of the plurality of contacts 210 a-210 h (andcorresponding pickups 208 a-208 h) are provided between each of theeight pairs of sides, as shown. For example, the representative pickup208 a may be diffused in the epi region 202 between the outer perimeterside 214 a and the inner perimeter side 216 a.

The substrate upon which the Hall effect element (e.g., the dual Halleffect element 200) is formed has a so-called Miller index (i.e., plane)that characterizes a direction of crystalline structures within thesubstrate. Miller indices and Miller directions are known and are notfurther taught herein. It is known that electrical currents tend tofavor a direction of travel in a substrate. In other words, inparticular directions of flow relative to a crystalline structure of asubstrate, a substrate has lowest plate resistance. For this reason andfor additional reasons described below, lines joining opposing pairs ofthe electrical contacts are in particular directions described morefully below.

The dual Hall effect element 200 has two sets of pickups (two sets offour pickups in this example). The first set includes pickups 208 a, 208c, 208 e, and 208 g and may correspond to the primary Hall effectelement 102 a of FIG. 1. The second set includes pickups 208 b, 208 d,208 f, and 208 h, and may correspond to the secondary Hall effectelement 102 b of FIG. 1. The first set of four pickups includes twoopposing pairs of pickups (e.g., pickups 208 a and 208 e, and pickups208 c and 208 g), either of which can be electrically coupled to theprimary amplifier 110 (FIG. 1) at a given time. Likewise, the second setof four pickups includes two opposing pairs of pickups (e.g., pickups208 b and 208 f, and pickups 208 d and 208 h), each of which can beelectrically coupled to the secondary amplifier 112 (FIG. 1) at a giventime.

The orientation of the pickups 208 may be selected such that pairs ofcontacts from the first set are oriented along lines at forty-fivedegree angles from pairs of contacts from the second set. For example,as shown in FIG. 2, pickups 208 a and 20 e 8 are orientated along oneline, pickups 208 b and 208 f are orientated along a different line, andthose lines are at a forty-five degree angle to each other.

In the example of FIG. 2, the primary and secondary Hall effect elements102 a, 102 b share a common magnetic field sensing layer (i.e., epilayer 202) and, thus, may have substantially the same magnetic fieldresponse in the absence of stress (i.e.,field_sensitivity₁≅field_sensitivity₂). However, because opposing pairsof pickups of the primary Hall effect element 102 a are orientedforty-five degrees relative to opposing pairs of pickups from thesecondary Hall effect element 102 b, the Hall effect elements 102 a, 102b will have different sensitivities to stress (i.e.,stress_sensitivity₁≠stress_sensitivity₂) due to Millerindices/directions and other crystallographic properties. In someembodiments, the primary Hall effect element 102 a is more sensitive tomechanical stress; in other embodiments, the secondary Hall effectelement 102 b is more sensitive to mechanical stress.

It will be appreciated from discussion above that, by measuring theoutput of both the primary and the secondary Hall effect elements 102 a,102 b, the stress state of the silicon may be deduced and appropriatecorrections made to the magnetic field sensor 100 output.

In some embodiments, the magnetic field sensor 100 of FIG. 1 uses a“chopping” technique. It will be understood that chopping is anarrangement by which at some times a selected pickup of a Hall effectelement is driven and at other times a different selected pickup isdriven. Similarly, at some times an output signal is generated between afirst pair of the pickups, and at other times an output signal isgenerated between the second pair of the pickups. The second pair ofpickups may be arranged along a line perpendicular to that of the firstpair of pickups. It will further be understood that the choppingarrangement is often used with planar Hall effect elements to result ina reduction of the DC offset voltage.

For a dual Hall effect element, such as the dual Hall effect element 102of FIG. 1, both the primary and secondary Hall effect elements 102 a,102 b may be “chopped.” For example, referring specifically to FIGS. 2and 2A, the primary Hall effect element 102 a may alternately be drivenvia opposing pairs of contacts 210 a and 210 e, and contacts 210 c and210 g. Likewise, the secondary Hall effect element 102 b may alternatedriven via opposing pairs of contacts 210 b and 210 f, and contacts 210d and 210 h. Such alternations may occur in unison, meaning the pickupsused to generate the primary output signal are alternated generally atthe same time as the pickups used to generate the secondary outputsignal.

It should be understood that the dual Hall effect element 200 shown inFIGS. 2 and 2A is merely one example of a dual Hall effect element foruse with the magnetic field sensor 100 of FIG. 1. Additional examplesare shown in FIGS. 3, 3A, 4, 4A, 5, and 5A and described below inconjunction therewith.

Referring to FIGS. 3 and 3A together, for which FIG. 3 shows a top viewof FIG. 3A, and in which like elements are shown having like referencedesignations, an illustrative dual Hall effect element 300 may be thesame as or similar to the dual Hall effect element 102 of FIG. 1. Theillustrative dual Hall effect element 300 may be fabricated similar todual Hall effect element 200, as described above in conjunction withFIGS. 2 and 2A. In particular, the dual Hall effect element 300comprises an N-type epi region 302 disposed over a substrate 303, aninner P-well region 304 implanted and diffused into the epi region 302,an outer P-well region 306 implanted and diffused into the epi region302 to form an outer horizontal boundary thereof, and a PBL structure307 diffused within the epi region 302 and over the substrate 303,wherein the PBL structure 307 joins/merges with the outer P-well region306 forming a barrier structure (or “isolation region”) 313.

The dual Hall effect element 300 includes a first set of pickups 308a-308 d implanted and diffused within the epi region 302 and a secondset of pickups 308 e-308 h implanted and diffused within the innerP-well region 304. In this example, opposing pairs of pickups from thefirst set (i.e., pickups 308 a and 308 c, and pickups 308 b and 308 d)are separated by the inner P-well region 304 and opposing pairs ofpickups from the second set (i.e., pickups 308 e and 308 g, and pickups308 f and 308 h) are diffused within the inner P-well region 304. Insome embodiments, each one of the first set of pickups 308 a-308 dcomprise an N+ type diffusion, whereas each one of the second set ofpickups 308 e-308 h comprise a P+ type diffusion. The dual Hall effectelement 300 further includes a plurality of contacts 310 a-310 h, eachof which is associated with one of the pickups 308 a-308 h. In theside-view of FIG. 3A, only pickups 308 a, 308 e, 308 f, and 308 b andrespective contacts 310 a, 310 e, 310 f, and 310 b are visible.

It will be appreciated that the illustrative dual Hall effect element300 is a dual planar (i.e., horizontal) Hall effect element.

The illustrative dual Hall effect element 300 includes a major planarsurface (shown in FIG. 3) having an outer perimeter 314 with a generallysquare shape. The perimeter 314 may be defined by edges of the epiregion 302 bounded by the isolation region 313. In addition, the dualHall effect element 300 includes an inner perimeter 316 also having agenerally square shape and being defined by a boundary between the innerP-well region 304 and the epi region 302.

In some embodiments, a pickup and corresponding contact are provided ateach corner of the outer perimeter 314, as shown.

The first set of pickups 308 a-308 d disposed within the epi region 302may correspond to the primary Hall effect element 102 a (FIG. 1),whereas the second set of pickups 308 e-308 h disposed within the innerP-well 304 may correspond to the secondary Hall effect element 102 b.Because the sets of pickups are disposed within different types ofmaterials, the magnetic field sensitivities of the corresponding primaryand secondary Hall effect elements will generally be different (i.e.,field_sensitivity₁≠field_sensitivity₂).

As with the illustrative dual Hall effect element 200 of FIG. 2, theprimary and secondary Hall effect elements corresponding to the dualHall effect element 300 are arranged so axes of maximum magnetic fieldsensitivity are parallel, centers of the two perimeters aresubstantially collocated, and both share a common isolation region.

Thus, by simultaneously obtaining differential Hall outputs from a firstpair of contacts disposed within N-type epi 302 and a second pair ofcontacts disposed within P-well 304, the stress state of the silicon maybe deduced and appropriate corrections made to the magnetic field sensor100 of FIG. 1.

As discussed above, a dual Hall effect element can be chopped. Referringto the dual Hall effect element 300 of FIG. 3, the primary Hall effectelement 102 a may alternately be driven via opposing pairs of contacts310 a and 310 c, and contacts 310 b and 310 d. Likewise, the secondaryHall effect element 102 b may alternately driven via opposing pairs ofcontacts 310 e and 310 g, and contacts 310 f and 310 h.

Referring to FIGS. 4 and 4A together, for which FIG. 4 shows a top viewof FIG. 4A, and in which like elements are shown having like referencedesignations, an illustrative dual Hall effect element 400 may be thesame as or similar to the dual Hall effect element 102 of FIG. 1.

The dual Hall effect element 400 includes magnetic field sensingstructures 400 a and 400 b provided over a common substrate 403. Invarious embodiments, the structures 400 a, 400 b are provided in stackedrelation and, thus, the structure 400 a is referred to herein as the“bottom structure” 400 a, whereas the other structure 400 b is referredto as the “top structure” 400 b.

The bottom structure 400 a may be fabricated similar to dual Hall effectelement 200, as described above in conjunction with FIGS. 2 and 2A. Inparticular, the bottom structure 400 a comprises an N-type epi region402 disposed over a substrate 403, an outer P-well region 406 implantedand diffused into the epi region 402 to form an outer horizontalboundary thereof, and a PBL structure 407 diffused within the epi region402 and over the substrate 403, wherein the PBL structure 407joins/merges with the P-well region 406 forming a barrier structure (or“isolation region”) 413. The bottom structure 400 a also includes afirst set of pickups 408 (with four pickups 408 a-408 d shown in thisexample) implanted and diffused into the epi region 402. In someembodiments, pickups 408 a-408 d from the first set comprise N+ typediffusions. The bottom structure 400 a further includes a first set ofcontacts 410 a-410 d, each of which is associated with one of thepickups 408 a-408 d.

In certain embodiments, the bottom structure 400 a includes an innerP-well region 404 diffused into the epi region 402, as shown. Opposingpairs of pickups from the first set of pickups (e.g., pickups 408 a and408 c, and pickups 408 b and 408 d) may be separated by the inner P-wellregion 404. As discussed above, such an arrangement can increase thesensitivity of a planar Hall effect element.

The top structure 400 b includes a top layer 418 and a second set ofpickups 408 e-408 h implanted and diffused therein. In some embodiments,pickups 408 e-408 h from the second set comprise an N+ type diffusion.In other embodiments, pickups 408 e-408 h from the second set comprise aP+ type diffusion. The top structure 400 b further includes a second setof contacts 410 e-410 h, each of which is associated with one of thepickups 408 e-408 h.

The top layer 418 may be comprised of any deposited material suitablefor detecting a magnetic field, such as such as a poly silicon (or “polygate”) material. During fabrication, the layer 418 may be spun onto thetop surface of the bottom structure 400 a.

The top structure 400 b is electrically isolated from the bottomstructure 400 a via a separation region 400 c (e.g., a separationlayer). In some embodiments, the separation region 400 c is provided asan oxide layer.

It will be appreciated that the illustrative dual Hall effect element400 is a dual planar (i.e., horizontal) Hall effect element.

The illustrative bottom structure 400 a includes a major planar surface(shown in FIG. 4) having an outer perimeter 414 with a generally squareshape. The perimeter 414 may be defined by edges of the epi region 402bounded by the isolation region 413. In addition, the bottom structure400 a includes an inner perimeter 416 also having a generally squareshape and being defined by a boundary between the inner P-well region404 and the epi region 402. In some embodiments, the first set of fourpickups 408 a-408 d and corresponding contacts are provided atrespective corners of the outer perimeter 414, as shown.

The illustrative top structure 400 b includes a major planar surface(shown in FIG. 4) having an outer perimeter 420 with a generally squareshape. The perimeter 420 may be defined by edges of the top layer 418.In some embodiments, the second set of four pickups 408 e-408 h andcorresponding contacts are provided at respective corners of the outerperimeter 420, as shown.

The first set of pickups 408 a-408 d disposed within the epi region 402may correspond to the primary Hall effect element 102 a (FIG. 1),whereas the second set of pickups 408 e-408 h disposed within the toplayer 418 may correspond to the secondary Hall effect element 102 b. Theprimary and secondary Hall elements 102 a, 102 b are overlaid with eachother such that the secondary Hall effect element lies within or over aperimeter of the primary Hall effect element, the perimeter defined byan outer boundary of an electrical isolation structure surrounding theprimary Hall effect element. Because the first and top structures 400 aand 400 b utilize different materials, the respective magnetic fieldsensitivities may differ (i.e., field_sensitivity₁≠field_sensitivity₂).

As with the illustrative dual Hall effect elements 200 and 300 of FIGS.2 and 3, respectively, the primary and secondary Hall effect elementscorresponding to the dual Hall effect element 400 are arranged so thataxes of maximum magnetic field sensitivity are substantially paralleland centers of the perimeters (i.e., centers between the two sets ofpickups 408 a-408 d and 408 e-408 h) are substantially collocated.However, it will be understood that, in contrast to the dual Hall effectelements 200 and 300, the primary and secondary Hall effect elementsdefined by the dual Hall effect element 400 do not share a commonisolation region.

Thus, by simultaneously obtaining differential Hall outputs from a firstpair of contacts disposed within epi region 402 and a second pair ofcontacts disposed within top layer 418, the stress state of the siliconmay be deduced and appropriate corrections made to the magnetic fieldsensor 100 of FIG. 1.

As discussed above in conjunction with FIG. 2, a dual Hall effectelement can be chopped. Referring to the dual Hall effect element 400 ofFIG. 4, the primary Hall effect element 102 a may alternately driven viaopposing pairs of contacts 410 a and 410 c, and contacts 410 b and 410d. Likewise, the secondary Hall effect element 102 b may alternatelydriven via opposing pairs of contacts 410 e and 410 g, and contacts 410f and 410 h.

Referring to FIGS. 5 and 5A together, for which FIG. 5 shows a top viewof FIG. 5A, and in which like elements are shown having like referencedesignations, an illustrative dual Hall effect element 500 may be thesame as or similar to the dual Hall effect element 102 of FIG. 1.

The dual Hall effect element 500 can be constructed over a substrate503, within and upon an epitaxial (“epi”) region (or “layer”) 502disposed upon the substrate 503. In the embodiments shown, the substrate503 is a P+ substrate and the epi region 502 is a P− epi region. AnN-well region 505 may be diffused into the P-type epi region 502, asshown. In some embodiments, the dual Hall effect element 500 includes aninner P-well region 504 diffused into the N-well region 505, as shown.

The dual Hall effect element 500 includes a first set of pickups 508a-508 d implanted and diffused within the N-well region 505 and, in someembodiments, a second set of pickups 508 e-508 h implanted and diffusedwithin the inner P-well region 504. In this example, opposing pairs ofpickups from the first set (i.e., pickups 508 a and 508 c, and pickups508 b and 508 d) are separated by the inner P-well region 504 andopposing pairs of pickups from the second set (i.e., pickups 508 e and508 g, and pickups 508 f and 508 h) are diffused within the inner P-wellregion 504. The dual Hall effect element 500 further includes aplurality of contacts 510 a-510 h, each of which is associated with oneof the pickups 508 a-508 h. In the side-view of FIG. 5A, only pickups508 a, 508 e, 508 f, and 508 b and respective contacts 510 a, 510 e, 510f, and 510 b are visible.

It will be appreciated that the dual Hall effect element 500 of FIG. 5is similar to the dual Hall effect element 300 of FIG. 3. However,whereas the Hall element 300 includes a N-type epi region into whichpickups are diffused, the Hall element 500 includes a P-type epi regionand an N-well region diffused into the epi region and into which pickupsare diffused. The N-well region 505 acts to “invert” the base materialtype into which the pickups are diffused (i.e., from P-type to N-type)and is thus sometimes referred to as an “N-type inversion layer.” Inaddition, the N-well serves creates an isolation region and thus abarrier structure (e.g., structure 313 in FIG. 3) is not required, asindicated by dashed lines in FIGS. 5 and 5A.

All references cited herein are hereby incorporated herein by referencein their entirety.

Having described certain embodiments, which serve to illustrate variousconcepts, structures and techniques sought to be protected herein, itwill be apparent to those of ordinary skill in the art that otherembodiments incorporating these concepts, structures, and techniques maybe used. Accordingly, it is submitted that that scope of the patentshould not be limited to the described embodiments but rather should belimited only by the spirit and scope of the following claims.

What is claimed is:
 1. A magnetic field sensor comprising: a substratehaving a bottom surface and a top surface; an epitaxial layer disposedover the top surface of the substrate, the epitaxial layer having a topsurface and a bottom surface, the bottom surface of the epitaxial layerproximate to and parallel to the top surface of the substrate; and adual Hall element, comprising: a first planar Hall element disposedwithin or over the epitaxial layer, the first planar Hall element havinga first plurality of pickups with a first center between the firstplurality of pickups; and a second planar Hall element disposed withinor over the epitaxial layer, the second planar Hall element having asecond different plurality of pickups with a second center between thesecond plurality of pickups, wherein a line intersecting the first andsecond centers is perpendicular to the top surface of the epi layer,wherein the first planar Hall element has a first sensitivity to amagnetic field and a first sensitivity to mechanical stress in thesubstrate, the first planar Hall element for generating a first outputsignal responsive to the magnetic field, the first magnetic fieldsensitivity, mechanical stress in the substrate, and the firstmechanical stress sensitivity, and wherein the second planar Hallelement has a second sensitivity to the magnetic field and a secondsensitivity to mechanical stress in the substrate, the second planarHall element for generating a second output signal responsive to themagnetic field, the second magnetic field sensitivity, the mechanicalstress in the substrate, and the second mechanical stress sensitivity.2. The magnetic field sensor of claim 1 wherein the epitaxial layercomprises an N-type epitaxial layer, wherein the dual Hall elementfurther comprises: a barrier structure disposed over the substrate andextending perpendicular from the epitaxial layer top surface so as toform a barrier to electrical charges within the epitaxial layer andresulting in a bounded region of the epitaxial layer having an octagonalshape; a P-well region diffused into the epitaxial layer; and aplurality of pickups implanted and diffused into the epitaxial layer,opposing pairs of the plurality of pickups separated by the P-wellregion, each one of the plurality of pickups comprising an N+ typediffusion, wherein a first set of the plurality of pickups is operableto form the first Hall element and a second different set of theplurality of pickups is operable to form the second Hall element.
 3. Themagnetic field sensor of claim 1 wherein the epitaxial layer comprisesan N-type epitaxial layer, wherein the dual Hall element furthercomprises: a barrier structure disposed over the substrate and extendingperpendicular from the epitaxial layer top surface so as to form abarrier to electrical charges within the epitaxial layer; a P-wellregion diffused into the epitaxial layer; a first plurality of pickupsimplanted and diffused into the epitaxial layer, opposing pairs of thefirst plurality of pickups separated by the P-well region, each one ofthe first plurality of pickups comprising an N+ type diffusion; and asecond plurality of pickups implanted and diffused into the P-wellregion, each one of the second plurality of pickups comprising an P+type diffusion, wherein the first plurality of pickups is operable toform the first Hall element and the second plurality of pickups isoperable to form the second Hall element.
 4. The magnetic field sensorof claim 1 wherein the epitaxial layer comprises an N-type epitaxiallayer, wherein the dual Hall element further comprises: a bottomstructure, wherein the bottom structure comprises: a barrier structuredisposed over the substrate and extending perpendicular from theepitaxial layer top surface so as to form a barrier to electricalcharges within the epitaxial layer; a P-well region diffused into theepitaxial layer; and a first plurality of pickups implanted and diffusedinto the epitaxial layer, opposing pairs of the first plurality ofpickups separated by the P-well region, each one of the first pluralityof pickups comprising an N+ type diffusion, wherein the magnetic fieldsensor further comprises: a top structure electrically isolated from thebottom structure via an isolation region, the top structure comprising atop layer; and a second plurality of pickups implanted and diffused intothe top layer, wherein the first plurality of pickups is operable toform a first Hall element and the second plurality of pickups isoperable to form a second Hall element.
 5. The magnetic field sensor ofclaim 1 wherein the epitaxial layer comprises a P-type epitaxial layer,wherein the dual Hall element further comprises: an N-well regiondiffused into the P-type epitaxial layer; a P-well region diffused intothe N-well region; a first plurality of pickups implanted and diffusedinto the N-well region, opposing pairs of the first plurality of pickupsseparated by the P-well region, each one of the first plurality ofpickups comprising an N+ type diffusion; and a second plurality ofpickups implanted and diffused into the P-well region, each one of thesecond plurality of pickups comprising an P+ type diffusion, wherein thefirst plurality of pickups is operable to form the first Hall elementand the second plurality of pickups is operable to form the second Hallelement.
 6. The magnetic field sensor of claim 1 wherein the epitaxiallayer comprises an N-type epitaxial layer.
 7. The magnetic field sensorof claim 1, further comprising: a stress compensation module coupled toreceive a first stress compensation input signal responsive to the firstoutput signal and a second stress compensation input signal responsiveto the second output signal and to generate a stress compensationsignal; and an adjustable gain stage coupled to amplify the first outputsignal with a gain in accordance with the stress compensation signal togenerate a stress-compensated output signal, wherein thestress-compensated output signal is responsive to the magnetic field,and is not responsive to the mechanical stress in the substrate.
 8. Themagnetic field sensor of claim 7 wherein the stress compensation moduleis configured to calculate the gain using only the first magnetic fieldsensitivity, the second magnetic field sensitivity, the first mechanicalstress sensitivity, the second mechanical stress sensitivity, the firstoutput signal, and the second output signal, wherein the stresscompensation signal is based upon the gain.
 9. The magnetic field sensorof claim 7 wherein the stress compensation module is configured tocalculate the gain using only the first magnetic field sensitivity, thesecond magnetic field sensitivity, the first output signal, and thesecond output signal, wherein the stress compensation signal is basedupon the gain.
 10. The magnetic field sensor of claim 7 wherein thestress compensation module is configured to calculate the gain using thefirst magnetic field sensitivity, the second magnetic field sensitivity,the first mechanical stress sensitivity, and the second mechanicalstress sensitivity, wherein the stress compensation signal is based uponthe gain.
 11. The magnetic field sensor of claim 7 the stresscompensation module is configured to calculate the gain using the firstmagnetic field sensitivity, the second magnetic field sensitivity, thefirst output signal, and the second output signal, wherein the stresscompensation signal is based upon the gain.
 12. The magnetic fieldsensor of claim 7 wherein the stress compensation module is configuredto calculate the gain using the first magnetic field sensitivity and thesecond magnetic field sensitivity, wherein the stress compensationsignal is based upon the gain.
 13. The magnetic field sensor of claim 7further comprising a first amplifier coupled to receive the first outputsignal and to generate the first stress compensation input signal and asecond amplifier coupled to receive the second output signal and togenerate the second stress compensation input signal.
 14. The magneticfield sensor of claim 13 wherein the first and second output signals areresponsive to a substrate temperature, wherein the first and secondstress compensation signals are not responsive to the substratetemperature.
 15. The magnetic field sensor of claim 13 furthercomprising a threshold detector coupled to receive a threshold levelsignal and a threshold detector input signal responsive to the firstoutput signal, the threshold detector configured to generate an enablingsignal based upon the threshold level signal and the threshold detectorinput signal.
 16. The magnetic field sensor of claim 15 wherein thestress compensation module is coupled to receive the enabling signal andconfigured to calculate the gain in response to the enabling signal. 17.A magnetic field sensor comprising: a first magnetic field sensingelement supported by a substrate, the first magnetic field sensingelement having a first sensitivity to a magnetic field and a firstsensitivity to mechanical stress in the substrate, the first magneticfield sensing element for generating a first output signal responsive tothe magnetic field, the first magnetic field sensitivity, mechanicalstress in the substrate, and the first mechanical stress sensitivity; asecond magnetic field sensing element supported by the substrate, thesecond magnetic field sensing element having a second sensitivity to themagnetic field and a second sensitivity to mechanical stress in thesubstrate, the second magnetic field sensing element for generating asecond output signal responsive to the magnetic field, the secondmagnetic field sensitivity, the mechanical stress in the substrate, andthe second mechanical stress sensitivity; a stress compensation moduleoperatively coupled to receive a first stress compensation input signalresponsive to the first output signal and a second stress compensationinput signal responsive to the second output signal and to generate astress compensation signal; and an adjustable gain stage coupled toamplify the first output signal with a gain in accordance with thestress compensation signal to generate a stress-compensated outputsignal, wherein the stress-compensated output signal is responsive tothe magnetic field, and is not responsive to the mechanical stress inthe substrate, wherein the first and second magnetic field sensingelements are provided as a dual Hall element comprising: a substratehaving a bottom surface and a top surface; an N-type epitaxial layerdisposed over the substrate top surface, the epitaxial layer having atop surface and a bottom surface; a barrier structure disposed over thesubstrate and extending perpendicular from the epitaxial layer topsurface so as to form a barrier to electrical charges within theepitaxial layer and resulting in a bounded region of the epitaxial layerhaving a generally octagonal shape; a P-well region diffused into theepitaxial layer, and a plurality of pickups implanted and diffused intothe epitaxial layer, opposing pairs of the plurality of pickupsseparated by the P-well region, each one of the plurality of pickupscomprising an N+ type diffusion, wherein a first set of the plurality ofpickups is operable to form the first magnetic field sensing element asa first Hall element and a second different set of the plurality ofpickups is operable to form the second magnetic field sensing element asa second Hall element.